This invention pertains to minimally invasive surgery of the lung. In particular, it applies to application of brachytherapy techniques directed primarily to lung or pleural tissue surfaces exposed by or created as a result of tumor resection or the presence of primary cancer of the pleura. As with other tumor resection procedures, and even when pathology shows “clear” margins, there is potential for disease recurrence from diffuse proliferative disease in the resected surfaces. Balloon brachytherapy as an adjuvant follow-up to resection has been shown to reduce the likelihood of such recurrent disease.
Recent advances in surgical treatment of proliferative diseases of the lung include endoscopic procedures conducted through, and directed to lesions near the bronchi, and alternatively, video-assisted, minimally-invasive thoracic surgery directed to more peripheral disease and performed through incisions providing access to the thoracic cavity.
Today with early stage carcinoma of the lung, particularly in peripheral portions of the lung, treatment consists of resecting a wedge-shaped portion of lung through small incisions between adjacent ribs. If a wedge resection is inadequate to excise the entirety of the tumor, a lobectomy may be performed, removing a complete pulmonary lobe. Visualization is provided by camera or conventional fiber optic means mounted on a thoroscope and monitor display, although other state-of-the-art modalities can be used. Percutaneous or other methods or small incisions are used to introduce the necessary instrumentation, and with newer, minimally invasive techniques, conventional rib spreading is not required. The absence of rib spreading greatly reduces pain and hastens patient recovery, but narrows instrument access to a few small, discrete points on the rib cage. In order to provide adjuvant brachytherapy, methods and apparatus are needed that are compatible with the methods described above, and preferably without requiring additional access beyond that already established during resection.
With the intrabronchial approach to treatment of obstructions or lesions, a flexible bronchoscope with a working channel is generally employed in the affected bronchus while the remaining bronchial tree provides intraoperative ventilation. The bronchoscope also comprises either camera or fiber optic means to provide monitor display. Other instrumentation, preferably including that for follow-up brachytherapy, must be flexible, and of appropriate diameter for operation from within the working channel in order to be compatible. Extra or intrabronchial procedures often involve removal of a diseased section of bronchus, after which the exposed ends are usually approximated, either by suture or staple methods. Adjuvant brachytherapy may also be indicated after extra or intrabronchial surgery.
Brachytherapy practice traditionally comprises positioning a radiation source within target tissue and delivering a therapeutic dose of radiation, often from within a balloon, without overdosing either target or adjacent tissue. One particularly useful class of radiation sources are miniature electronic x-ray tubes which may be switched on and off at will, or which can be modulated with respect to either penetration depth (by controlling acceleration voltage of the x-ray tube) or dose intensity (by controlling filament current). These tubes are usually mounted at the end of a power supply cable and can emit isotropically or can be directional, emitting through a predetermined solid angle. One reference describing the principles and construction of such tubes is Atoms, Radiation and Radiation Protection, Second Edition, John E. Turner, Ph.D., CHP, 1995, John Wiley & Sons, Section 2.10. By contrast, isotope sources cannot in principle be modulated, and in addition require both isolation of the patient during radiotherapy and special facilities and apparatus to assure safety of personnel.
A minimum therapeutic absorbed dose (the prescription dose) is selected by the therapist to be delivered to all of the target tissue. Because dose generally decreases exponentially with distance from the source, accurate dose delivery is complicated and automated treatment planning is generally employed to assure delivery of a dose to the target tissue which is at least equal to the prescription dose, but which is also within allowable limits, thus avoiding substantial necrosis of normal tissue. The prescription dose may of necessity vary depending on the proximity of the source to radiation sensitive structures within the anatomy. Examples would include the skin, heart or other organs, and bone. Treatment planning is usually automated based on known radiation source parameters, prescription parameters, and geometry as determined by conventional imaging of the apparatus within tissue. Planning usually precedes the treatment delivery.
A useful device for controlling radiation intensity is an applicator, preferably a balloon applicator. Balloon applicators generally determine the interior shape of the target tissue (the resection cavity) and position the radiation source at a controlled distance from the tissue to be treated, thus defining treatment geometry and reducing the radiation intensity exponentially from spatial considerations. Several other means are available to moderate the absorbed dose delivered to the tissue. As noted above, the acceleration voltage applied to the x-ray tube can be used to limit the penetration depth of the radiation. The filament current can be reduced to lower emitted intensity, or in fact, to eliminate emissions altogether. Once output emission characteristics are determined by selection of x-ray tube input parameters, shielding can be used to reduce radiation intensity, or to control the direction of emissions, statically or dynamically as therapy progresses. Such shielding and attenuation methods for x-ray tubes are described in copending application Ser. Nos. 11/385,255, 11/471,277 and 11/471,013, each of which is incorporated herein in their entirety by reference.
Balloon applicators are known, for example those described in U.S. Pat. No. 6,413,204. In general, such applicators comprise a balloon mounted on a shaft proximate the distal end of the shaft, and further comprise at least one source guide to position the source at a known distance or distances from the balloon (and tissue cavity) surface. Fluid circuits can be provided communicating from outside the patient to the interior of the balloon for inflation purposes, or to outside the shaft and/or balloon for example for suction purposes or administration of anesthetic or therapeutic agents.